1. Field of the Invention
The present invention relates to a repair coating process in order to form multilayer coating films with excellent highly white pearl luster effect, color stability etc.
2. Description of the Related Art
It is already known to form multilayer coating films on an outer panel of a car body etc. by coating with an electrodeposition paint and an intermediate paint and, after curing them, by wet-on-wet coating on the intermediate coating surface with topcoat paints such as a white type water base coat capable of forming a coating film adjusted in the range of Munsell Color Chart N7-N9 with titanium white pigment and aluminium flake, a pearly base coat formed by compounding flake-like mica powder coated with titanium oxide and a clear coat etc., and then by curing by crosslinking these 3-layer coating films simultaneously through heating (for example, U.S. Pat. No. 5,718,950).
In a coating line to form these multilayer coating films on an outer panel of a car body etc., dust may adhere or seediness like projection etc. may generate on the intermediate coating surface and if a topcoat paint is coated as such, finished appearance like smoothness etc. declines which is undesirable. Therefore, it is necessary to previously remove such dust, seediness etc.
Concretely speaking, on the cured intermediate coating film, a part of the coating surface around the point, on which dust, seediness etc. is adhered, is ground spot-wise to remove them. By the grinding usually 20 xcexcm or more depth of the intermediate coating film (and sometimes a part of the electrodeposition coating film, too) is removed. To the ground part then a repair coating is performed.
As a repair coating process of the ground part there can be mentioned, for example, i) a process to coat a white type water base coat, which would be used at the next step, to the ground part and, leaving it at an uncured state without heat-curing, to coat the same white type water base coat on the whole surface to be coated, ii) a process to coat the intermediate paint, which was used at the previous step, to the ground part and, after curing it by heating, to coat a white type water base coat on the whole surface to be coated, and others.
However, the above-mentioned process i) has a drawback of being prone to generate blistering and/or popping, because the total film thickness of the white type water base coat at the ground part is thicker than that at other unground parts, although a heating step of the repair coating film can be saved. The above-mentioned process ii) does not have such a drawback as mentioned above, but is not favorable in view of shortening process steps, because it contains a heating step.
The main aim of the present invention is to provide a repair coating process, which does not require a heating step and does not generate blistering and/or popping, at the ground part of an intermediate coating film, on which dust, seediness, etc. adhered during a process of forming multilayer coating films by coating a topcoat paint such as a white type water base coat, a pearly base coat, a clear coat etc, on a heat-cured intermediate coating surface by a 3-coat-1-bake process, and its characteristic exists in performing a repair coating to the ground part of an intermediate coating film using a specific hydrophilic organic solvent type paint.
Namely, the present invention provides a repair coating process of multilayer coating films characterized by grinding the part of an intermediate coating surface to be repaired and then performing a repair coating of the ground part with a thermocurable organic solvent type repair paint (F) containing a neutralized product of a hydroxyl group-containing resin having an acid value of 5-100 mgKOH/g and a crosslinking agent in forming multilayer coating films by coating an electrodeposition paint (A) and an intermediate paint (B) and curing them by heating, then, after performing a repair coating on the intermediate coating surface, by successively coating wet-on-wet a white type water base coat (C) capable of forming a coating film adjusted the Munsell Color Chart to be in the range of N7-N9 with titanium white pigment and aluminium flake, a pearly base coat (D) formed by compounding flake-like mica powder coated with titanium oxide and a clear coat (E), and then by curing by crosslinking the films of the above-mentioned coats (C), (D) and (E) simultaneously through heating.